1. Why Orientation Is the First Design Decision

Every solar calculation — panel count, battery size, cable gauge, inverter rating — is built on one number: how many kilowatt-hours (kWh) can your array realistically produce per day? That number is determined almost entirely by three factors:

1. Panel direction (azimuth) — which compass bearing your panels face
2. Panel tilt angle — the angle between your panels and the horizontal ground
3. Shading — obstructions that block sunlight during key hours

Get these three wrong and even the most expensive panels and best batteries will underperform. Get them right and even a modest system will reliably power your home.

2. Understanding the Sun’s Path

The sun rises in the east, travels across the sky, and sets in the west — but how high it rises and exactly where it rises changes every day of the year. Two angles define the sun’s position at any moment:

Solar Azimuth (Compass Direction)

The solar azimuth is the compass bearing of the sun, measured clockwise from true north. At solar noon — when the sun is at its highest point — the azimuth is exactly 180° (due south) for locations north of the equator, and exactly 0°/360° (due north) for locations south of the equator.

Solar Altitude (Elevation Angle)

The solar altitude is how high the sun is above the horizon, measured in degrees. At sunrise and sunset it is 0°. At solar noon it reaches its peak — the higher the altitude, the more direct (and powerful) the sunlight hitting your panels.

Solar Declination and Seasons

The Earth’s axis is tilted 23.5° relative to its orbit. This causes the sun to appear higher in the sky in summer and lower in winter. On the equinoxes (around March 21 and September 21), the sun rises due east and sets due west — everywhere on Earth. On the December solstice, the sun is furthest south; on the June solstice, furthest north.

Date	Sun’s Position at Noon	Effect in Sub-Saharan Africa
March/Sept Equinox	Directly overhead at equator	Maximum intensity near-equator regions
June Solstice	23.5°N (Tropic of Cancer)	Lower sun angle in southern Africa, higher in East Africa
December Solstice	23.5°S (Tropic of Capricorn)	Higher sun angle in southern Africa; rainy season in East Africa

3. Latitude: Your Most Important Number

Your latitude — your distance north or south of the equator — determines everything about optimal panel positioning. It tells you:

• The maximum angle the sun reaches at noon
• Your optimal panel tilt angle
• The direction your panels should face
• How much seasonal variation your system will experience

Simple rule: Your optimal fixed tilt angle ≈ your latitude in degrees.

For locations within 5° of the equator (like Kampala, Nairobi, or Kigali), even a 5–10° tilt works well — primarily to allow rainwater runoff and self-cleaning. At 30° south like Johannesburg, panels should tilt 30° and face due north.

City	Country	Latitude	Panel Direction	Recommended Fixed Tilt
Kampala	Uganda	0.3°N	South (slight preference)	5–10°
Nairobi	Kenya	1.3°S	North (slight preference)	5–10°
Kigali	Rwanda	1.9°S	North	5–10°
Accra	Ghana	5.6°N	South	6–12°
Lagos	Nigeria	6.5°N	South	7–12°
Addis Ababa	Ethiopia	9.0°N	South	9–15°
Dar es Salaam	Tanzania	6.8°S	North	7–13°
Lusaka	Zambia	15.4°S	North	15–20°
Harare	Zimbabwe	17.8°S	North	18–23°
Johannesburg	South Africa	26.2°S	North	26–31°
Cape Town	South Africa	33.9°S	North	34–39°

4. True North vs Magnetic North — A Critical Distinction

A phone compass or handheld compass points to magnetic north — not true north. The difference between the two is called magnetic declination, and in parts of Africa it can be significant enough to meaningfully reduce your system’s output if ignored.

In southern Africa, magnetic declination varies from about −15° to −25° (meaning magnetic north points 15–25° west of true north). If you align your panels to magnetic north in Cape Town without correction, your panels will be pointing about 25° off true north — losing an estimated 3–7% of annual yield.

How to correct for magnetic declination:

1. Find your location’s declination at ngdc.noaa.gov/geomag
2. If declination is −20° (westerly), your true north is 20° clockwise from your compass reading
3. Alternatively, use a GPS-based compass app (most modern smartphones correct automatically when GPS is on)

City	Magnetic Declination (approx. 2026)	Correction to Find True North
Nairobi, Kenya	−1.5°	Rotate 1.5° clockwise from compass N
Lagos, Nigeria	−2.0°	Rotate 2° clockwise
Addis Ababa, Ethiopia	+3.0°	Rotate 3° anti-clockwise
Lusaka, Zambia	−10.5°	Rotate 10.5° clockwise
Harare, Zimbabwe	−14.0°	Rotate 14° clockwise
Johannesburg, S. Africa	−22.5°	Rotate 22.5° clockwise
Cape Town, S. Africa	−25.5°	Rotate 25.5° clockwise

5. Peak Sun Hours (PSH) — The Number That Drives Every Calculation

Peak Sun Hours (PSH) is the single most important solar resource number for system design. It represents the equivalent number of hours per day at which solar irradiance equals 1,000 W/m² — the standard test condition intensity. A location with 5.5 PSH receives the same total solar energy in a day as 5.5 hours of full noon sunlight.

PSH is not the same as daylight hours. Nairobi has about 12 hours of daylight but only 5.5 PSH — because morning and evening sun is weaker, and some days are cloudy. PSH is a year-round daily average accounting for weather, seasons, and atmospheric conditions.

Africa, remarkably, contains some of the world’s highest PSH zones. The Sahel belt (Mali, Niger, Chad, Sudan) averages 6.5–7.5 PSH — exceptional for solar. Even equatorial zones with cloud cover average 4.5–5.5 PSH, still significantly higher than most of Europe or North America.

City	Average PSH (Annual Daily)	Worst Month PSH	Best Month PSH
Nairobi, Kenya	5.5	4.2 (July)	7.0 (Feb)
Kampala, Uganda	5.3	4.0 (Nov)	6.5 (Jan)
Kigali, Rwanda	4.9	3.8 (Apr)	6.3 (Aug)
Lagos, Nigeria	4.8	3.5 (Aug)	6.5 (Jan)
Accra, Ghana	5.0	3.6 (Aug)	6.8 (Feb)
Addis Ababa, Ethiopia	6.0	4.5 (Aug)	7.5 (Nov)
Dar es Salaam, Tanzania	5.6	4.2 (Jun)	7.0 (Oct)
Lusaka, Zambia	6.2	4.8 (Jun)	7.8 (Sep)
Harare, Zimbabwe	6.0	4.5 (Jun)	7.5 (Sep)
Johannesburg, S. Africa	5.5	4.0 (Jun)	7.0 (Oct)
Cape Town, S. Africa	5.2	3.5 (Jun)	7.5 (Dec)
Abuja, Nigeria	5.8	4.2 (Aug)	7.5 (Jan)

Data sourced from PVGIS (European Commission Joint Research Centre) and NASA POWER database. Always verify with PVGIS for your specific coordinates before finalising a design.

Why the Worst Month Matters Most

For an off-grid system, your design must be able to meet your load in the worst month — not the best or average. If you size for the average, your system will run short of power during wet season or winter months. Diaspora Solar always designs to the worst-case monthly PSH to ensure year-round reliability.

6. Shading: The Silent Destroyer

No orientation discussion is complete without addressing shading. Shade is the most destructive performance factor in any solar system — and it is irreversible once panels are installed in the wrong place.

How Shading Destroys Output

Standard solar panels are wired in series strings — meaning the electrical current flows through each panel in sequence. When one panel in a string is shaded, it acts like a kink in a hose: the current through the entire string is limited to that of the weakest panel. A single partially shaded panel can reduce a 10-panel string’s output by 50–80%.

Even a thin tree branch shadow, a satellite dish shadow, or a chimney casting shade for just 2 hours daily can devastate annual energy production.

The Golden Shading Rule

No shadow should fall on any part of your solar array between 9:00 AM and 3:00 PM solar time, on the worst day of the year (winter solstice). This is the minimum unshaded window. The wider you can extend it, the better your annual output.

How to Assess Shading on Site

1. Horizon scan: Stand at the proposed panel location. Use a compass to note any objects (trees, walls, buildings, tanks, poles) that break the horizon between east-southeast (120°) and west-southwest (240°) azimuth.
2. Sun path overlay: Use the SunCalc app (suncalc.org) to overlay your horizon scan with the sun’s path across all seasons. Any object that intersects the sun’s path between 9am–3pm is a shading problem.
3. Shadow stick test: Plant a stick vertically in the ground at the proposed panel location on the winter solstice (June 21 in southern hemisphere, December 21 in northern hemisphere). Observe shadows from 8am–4pm. Any shadow falling in the panel zone is a risk.
4. PVGIS horizon tool: Upload your location to PVGIS and use the horizon tool to quantify shading losses automatically.

Solutions When Shading is Unavoidable

• Micro-inverters: Each panel has its own inverter — shade on one panel doesn’t affect others. Increases cost but maximises yield in shaded environments.
• Power optimisers (DC optimisers): Mounted per panel, they allow each panel to operate at its own maximum power point. Works with a central inverter.
• East-west split array: Rather than all panels facing one direction, split the array — some east, some west. Reduces the chance that a single shade event affects the full system.
• Relocation: Sometimes the only real fix is moving the array — to a higher roof section, a different face of the building, or a ground mount position clear of obstructions.

7. Roof vs Ground Mount — Orientation Trade-offs

Roof-Mounted Systems

The most common installation type in urban and peri-urban Africa. The main constraints:

• Roof pitch: Ideal roof pitch in most of Africa (5–20°) is close to optimal tilt — a genuine advantage. Corrugated iron sheet roofs at 10–15° pitch facing the right direction require minimal additional mounting hardware.
• Roof direction: Many homes in Africa have east-west ridge lines, meaning the main roof faces north and south — ideal. Where roofs face east-west (ridge running north-south), consider an east-west split array, or elevate panels to face correctly using tilted frames.
• Roof material: Metal sheet roofs allow easy mounting with clamps and rails. Concrete slab roofs require ballasted frames (no penetration) or drilled anchors. Tile roofs need tile hooks — avoid cracking tiles with improper mounting.
• Structural load: A solar panel and mounting frame adds approximately 15–25 kg/m². Always assess the roof’s structural capacity, especially for older homes with timber rafters.

Ground-Mounted Systems

Ground mounts offer the greatest design flexibility and are often the best choice for rural, agricultural, and larger commercial installations.

• Full orientation control: Set any tilt angle and azimuth regardless of building orientation
• Single-axis tracking: Motorised frames that follow the sun east to west — increases output by 15–25% versus fixed mount
• Easier maintenance: No ladder required; easier cleaning and inspection
• Cooling: Air flows under panels, keeping them cooler and more efficient (panels lose ~0.4% efficiency per °C above 25°C)
• Disadvantages: Requires land, security fencing, longer cable runs, and vegetation management beneath

8. Seasonal Tilt Adjustment — Worth It?

For most of sub-equatorial Africa, a fixed tilt at latitude captures 95–97% of the maximum possible annual energy. Adjusting the tilt angle twice a year (summer and winter positions) typically adds only 5–8% more energy annually — rarely worth the labour and mechanical complexity for off-grid residential systems.

Exception: If your load is seasonal — for example, irrigation pumping only in dry season — optimise your tilt for that season’s sun angle rather than the annual average. For a dry-season irrigation load in southern Africa, a steeper winter tilt of latitude + 15° will maximise output exactly when you need it most.

Tilt Strategy	Annual Yield	Best For
Fixed at latitude	Baseline (100%)	All-year loads; simplest and most reliable
Fixed at latitude + 15°	~97–98% (worse in summer)	Dry-season only loads; winter-heavy consumption
Fixed at latitude − 15°	~97–98% (worse in winter)	Wet-season loads; summer-heavy consumption
Adjustable (2× per year)	~105–108%	Maximising yield; grid-tied commercial systems
Single-axis tracking	~120–125%	Large commercial; when land is available

9. The Azimuth Penalty — How Much Does Off-South/North Facing Cost?

What happens if your roof doesn’t face true south or north? The answer depends on how far off you are:

Deviation from True South/North	Approximate Annual Yield Loss	Practical Impact
0° (True south/north)	0%	Optimal — full annual yield
15° off	1–2%	Negligible — acceptable
30° off	4–6%	Minor — still good performance
45° off (SE or SW / NE or NW)	8–12%	Noticeable — add 10% more panels to compensate
90° off (True East or West)	20–30%	Significant — only viable with east-west split or oversizing
180° off (North-facing / South-facing away)	35–50%	Poor — avoid; system will underperform severely

The key takeaway: within 30° of optimal azimuth is acceptable with minor compensation. Beyond 45° off, you need to either reorient the array, split it, or significantly oversize to meet your load — which drives up cost.

10. Complete Site Assessment Checklist

Before engaging any solar designer or installer, walk through this checklist yourself. The more information you bring to the first meeting, the more accurate your system design will be — and the fewer expensive surprises during installation.

Location & Solar Resource

• ☐ Record GPS coordinates (latitude, longitude) using phone GPS
• ☐ Look up Peak Sun Hours for your location on PVGIS or NASA POWER
• ☐ Note the worst-month PSH (this drives your battery sizing)
• ☐ Find magnetic declination for your location (NOAA calculator)

Orientation & Tilt

• ☐ Measure roof or ground mount azimuth with compass + apply declination correction
• ☐ Record roof pitch/tilt angle (use a digital inclinometer app)
• ☐ Compare available orientation to optimal (latitude-based) tilt and azimuth
• ☐ Calculate estimated yield penalty if orientation is off-optimal

Shading Assessment

• ☐ Perform horizon scan: identify all objects breaking the skyline between E-SE and W-SW
• ☐ Map seasonal shading using SunCalc or SolarPathfinder
• ☐ Confirm no shade on array from 9am–3pm on winter solstice
• ☐ Document any unavoidable shading and consider micro-inverter or optimiser solutions

Structural & Physical

• ☐ Measure available roof/ground area (m²) for panel placement
• ☐ Assess roof structural condition (check rafters, purlins, fixings)
• ☐ Identify roof material (metal sheet, tiles, concrete slab, thatch)
• ☐ Estimate cable run distance: panels to charge controller/inverter to battery bank
• ☐ Identify proposed battery and inverter location (cool, ventilated, secure space)

What Comes Next: System Sizing & Design Calculations

With your site properly assessed — orientation confirmed, PSH known, shading documented — you now have the foundation for accurate system sizing. In Part 3 of this series, we will cover:

• How to calculate your daily energy load (Wh/day)
• Panel array sizing from PSH and load data
• Battery bank sizing for autonomy days
• Charge controller sizing (PWM vs MPPT)
• Inverter sizing for peak loads
• Wire sizing and voltage drop calculations
• A worked example: complete off-grid system for a 3-bedroom home in Nairobi

← Part 1: Why Solar Systems Fail — And How to Build One That Lasts